Apparatus for manufacture of laminated parts

ABSTRACT

Elongated thin strip stock is blanked to form interlocking laminas for electric motor or generator rotors or stators at successive blanking stations. At a final assembly station the laminas are stacked and pressed into interlocking relationship. In response to an operator input a predetermined number of reversals, or half turns about the stack axis of the previously stacked lamina are provided in order to compensate for nonuniform strip thickness to obtain a rotor or stator of substantially uniform height. Alternatively the thickness of the strip stock is gauged at transversely spaced points on the strip to determine cross feed thickness variation in the strip whereupon the stacked laminas are automatically provided with a number of reversals about the stack axis in response to a thickness differential that would result in a parallelism error in the stack that exceeds a predetermined amount. Rotor conductor slots are formed in the stacked laminas and are skewed to the stack axis by providing arcuate indexing of each lamina relative to the next preceding lamina in the stack by an arcuate increment that is automatically determined in response to operator entered inputs relative to the stack height, the skew angle, nominal lamina thickness and skew direction.

This is a division of U.S. application Ser. No. 08/335,137, filed Nov.7, 1994, now abandoned, which was a continuation of U.S. applicationSer. No. 07/874,860, filed Apr. 28, 1992 now U.S. Pat. No. 5,373,362,which is a division of U.S. application Ser. No. 07/724,866, filed onJul. 2, 1991, now U.S. Pat. No. 5,123,155, which is a continuationapplication of my U.S. application Ser. No. 07/171,555, filed Mar. 22,1988, entitled "METHOD FOR MANUFACTURE OF LAMINATED PARTS", now U.S.Pat. No. 5,087,849, which is a continuation of my U.S. patentapplication Ser. No. 06/853,207, filed Apr. 17, 1986, now U.S. Pat. No.4,738,020, which in turn is a divisional application of my U.S. patentapplication Ser. No. 06/478,692, filed Mar. 25, 1983, now U.S. Pat. No.4,619,028.

BACKGROUND OF THE INVENTION

This invention is in the field of laminated parts and their manufactureand more particularly electric motor or generator rotors and statorshaving stacked laminas and their manufacture.

Rotor and stator manufacture employing stacked laminas is well known inthe art. Typically, the laminas are blanked from continuous strip stockand then stacked and bound together to form the rotor or stator.However, due to manufacturing tolerance thickness variations of thestrip stock the rotor or stator could have a parallelism error, i.e. beout of conformance from a true right cylinder, thereby limiting closetolerance assembly of a rotor and a stator and operation thereof. Thisparallelism error occurs because in stacking the laminas the thickerportions of the laminas are directly overlying resulting in one side ofthe stack being higher than the opposite stack side causing a leaning orbending of the stack.

Also, in laminated rotor or stator manufacture a plurality of conductorslots are formed around the periphery of the rotor or stator stack inarcuately spaced relation to one another. If it is desired to skew theslot axes relative to the stack axis, it is common practice to indexeach lamina an arcuate increment relative to the next preceding laminaso that in a stack the axis of each slot is skewed or slanted relativeto the stack axis. The amount of indexing has been achieved by manuallyoperated clamps after the stack has been formed and by a manuallyadjustable stop which controls the degree of arcuate travel in eachrotational increment. Other prior art systems are evidenced by thestatements made in documents cited in the prosecution of thisapplication. Due to the inexactness of the above described manualadjustments, skew inaccuracies and/or excessive adjustment timeresulted. Other prior art systems are evidenced by the statements madeand documents cited in the prosecution of the aforementioned U.S. Patentand copending application from which this application is a continuation.

SUMMARY OF THE INVENTION

In a laminating press, laminas are blanked from elongated strip stockfor electric motor parts such as rotors or stators. The laminas arestacked or overlaid to form a lamina stack. One or more stack reversals,i.e. half turn rotations about the stack axis, are preformed just priorto stacking the next lamina. The number of reversals in each stack maybe selected and entered by the operator prior to press operation basedon known or experienced thickness variations in the strip stock. Themethod of this invention will then automatically provide the enterednumber of stack reversals at determined vertically spaced places in thestack height. Alternatively, the particular reversals may beautomatically selected by measuring the cross-feed or cross-graindifferential thickness of the strip stock. Cross-feed differentialthickness is defined as the thickness differential between at least twopoints along a transverse line substantially perpendicular to thelongitudinal feed direction of the strip stock. When the cross-feedthickness differential at a longitudinal portion on the strip stock isexcessive, as determined from certain later explained parameters, anumber of compensating stack reversals are automatically determined. Inthis manner, compensation is provided for nonuniform strip stockthickness.

To accurately obtain a predetermined skew angle of conductor slots inthe rotor lamina stack, the operator enters the stack height, thedesired skew angle, skew direction and nominal lamina thickness. Theskew direction is + (plus) or - (minus) depending whether the skew angleis clockwise or counterclockwise from the stack axis, respectively. Thenominal lamina thickness is the average thickness of the strip stock.This invention provides for accurately indexing each lamina an arcuateincrement relative the next previous lamina prior to stacking toaccurately obtain the desired skew angle.

The above mentioned half turn and indexing are achieved by a servomotorgear drive of a choke die which holds the stacked laminas. Theinstantaneous or actual rotational position of the die is compared withthe desired rotational position of the die as determined by thisinvention. An error signal corresponding to the differential of theactual and desired rotational positions is used to drive the servomotorto achieve the desired rotational position of the die prior to stackingthe next lamina.

It therefore is an object of this invention to provide a system forcompensating for nonuniform thickness of strip stock from which stackedlamina electric motor or generator parts are fabricated.

It is an object of this invention to provide in the system of theprevious object stack reversals about the stack axis, the number ofreversals being operator entered prior to the stacking or automaticallydetermined in response to measured cross-feed thickness of the stripstock.

It is a further object of this invention to index each lamina in alaminated stack of an electric motor or generator part having skewedconductor slots in response to operator entered inputs of stack height,a skew angle and nominal lamina thickness to accurately obtain a desiredconductor slot skew angle.

Another object is to provide laminated parts manufactured according tothe aforestated objects.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is an enlarged plan view of a rotor core;

FIG. 2 is a perspective view of a FIG. 1 rotor core;

FIG. 3 is a simplified, partially broken away, vertical section of a dieassembly for producing the core of FIG. 2;

FIG. 3A is a simplified, partially broken away, diagrammatic elevationalview of the gauge that is partially shown in FIG. 3;

FIG. 3B is a simplified, partially broken away, diagrammatic plan viewof the gauge of FIG. 3A;

FIG. 3C is an enlarged partial elevational view of the lower end area ofa punch pin at Station No. 4 in FIG. 3;

FIG. 3D is an enlarged view of the circled area in FIG. 3;

FIG. 4 is a plan view of the strip stock used in the die assembly ofFIG. 3 showing the blanking operations performed at each station in thepress of FIG. 3 with hatch shading showing the openings blanked at eachstation to distinguish the openings blanked at previous stations;

FIG. 5 is a simplified perspective diagrammatic view of the die assemblyand control system of this invention;

FIG. 6A is an exaggerated enlarged fragmentary elevational view of aconventional core stack;

FIG. 6B is a view similar to the view of FIG. 6A showing a core stack ofthis invention;

FIG. 6C is a view similar to the view of FIG. 6B showing another corestack of this invention;

FIG. 7 is a partial, broken elevational view of a second thickness gaugeembodiment for use with the press of FIG. 4; and

FIG. 8 is a partial view of a section taken at 8--8 of FIG. 7.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate a preferred embodiment of the invention, in one form thereof,and such exemplifications are not to be construed as limiting the scopeof the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2 a laminated rotor core 20 formed of aplurality of laminas 22 is shown. Each lamina 22 has a plurality ofteardrop shaped slot openings 24 spaced about and adjacent itsperimeter; a plurality of skew control holes 26 arcuately spaced about acircular arc that is spaced inwardly from the lamina perimeter; aplurality of oblong vent openings 28 arcuately spaced about a circulararc that is spaced further inwardly from the perimeter; and a centralshaft hole 30 having central axis 32. A counterbore 33 is formed in thelower end of core 20. Each lamina 22 excepting the bottom lamina in acore 20 has arcuate interlock tabs 34 depressed from the lamina lowersurface to engage a corresponding tab 34 and hole 26 in the next lowerlamina 22 to interlock the two laminas in a manner well known in theart. The bottom lamina 22, or first lamina, in the core 20 stack has theinterlock tab 34 areas blanked and removed since, as will becomeapparent, it is not desired to interlock the bottom lamina 22 to thelamina next below it, which is the top lamina in the preceding core, inorder that the cores are separate from one another.

Each lamina 22 is arcuately displaced about axis 32 from the lamina nextbelow it before the two laminas are interlocked in a manner such thatslots 38 are formed by openings 24 so that each of the slot 38 axes isprovided with a desired skew angle to axis 32 for purposes well known inthe art. Typically, slots 38 are filled with a molten electricallyconductive metal such as aluminum and are connected at their ends in amanner to provide rotor core conductor bars, as is well known in theart. The skew angle may be left handed or right handed depending onwhether the slot 38 axes cross axis 32 from left to right or right toleft as one moves downwardly down the slot axes.

Referring to FIGS. 6A and 6D an important function performed by thisinvention will be described. When laminas 22 are blanked from a strip40, FIG. 4, that has nonuniform thickness in the cross feed or crossgrain direction, a core 20, FIG. 6A, could result. As used herein, crossfeed or cross grain is a direction along a line that is perpendicular tothe feed direction or length of strip 40, such as line A-B in FIG. 3Band nonuniform thickness refers to the condition wherein one edge 40A ofstrip 40 is thicker than the opposite edge 40B in the cross feeddirection and is frequently present in available metal strip stock. Core20 has an error "d" which is a deviation from a true right cylinder andresults from the thicker edges of laminas 22 being vertically superposedone upon another and a parallelism error E_(p) which is the differencein heights of diametrically opposite sides of core 20 and is referred toherein to define the maximum permissible core 20 error that ispermissible for a given application. By providing a selected number ofstack rotations, or reversals, of 180°, each reversal prior tointerlocking the next lamina on the stack, the thicker edges may bealternated with the thinner edges to provide a true right cylinder, FIG.6B, and thus correct the error E_(p). In practice, it is often necessaryto half turn or reverse only once, FIG. 6C, in an entire core 20 toprovide a core stack with an acceptable parallelism error. In thisinvention the number of reversals may be preset and entered by theoperator prior to core manufacture or automatically determined by actualmeasured thickness variations of opposite edges of the strip 40 duringmanufacture.

Referring now to FIGS. 3, 3A, 3B, 3C, and 4, a blanking and core formingassembly 42 for the progressive blanking of an elongated stock strip 40to form laminas 22 and core 20 will be described. The blanked or formedportions of strip 40 at each of the following described stations isshown with a cross hatch shading to distinguish over those portionsblanked at previous stations. Briefly, at Station No. 1, holes 26, shaftpilot hole 44 and pilot holes 46 are blanked. At Station No. 2, thirtyfour slot openings 24 and six vent openings 28 are blanked. At StationNo. 3, a cluster of punch pins blank six interlock tab openings 48 forthe first, or bottom, lamina 22 only in a core 20 and a counterborepunch blanks a counterbore opening 49 in a specified number of laminas22 to form counterbore opening 33. At Station No. 4 arcuate interlocktabs 34 are lanced from strip 40 and then depressed below the lowerstrip surface, a tab 34 being adjacent each hole 26 and having itsdepressed end immediately below the edge of the corresponding hole 26,FIG. 3. At Station No. 5 a lamina 22 is blanked from strip 40, and shafthole 30 is simultaneously blanked, after which lamina 22 is pushed backinto the plane of strip 40. At Station No. 6, a lamina 22 is pushedthrough strip 40 and into a choke ring die barrel which is rotated anangular increment to obtain the desired skew angle and direction of theaxes of slots 38 and is rotated an additional 180° or half turn tocompensate for thickness nonuniformity of strip 40.

Strip 40 is fed from a supply coil or other supply, not show, and entersthickness gauge 50. Briefly described with reference to FIGS. 3, 3A, and3B, gauge 50 has vertically spaced carbide rollers 51, 52 rotatable onprecision ball bearings about horizontal, transverse axles 53A, 53Brespectively, above and below strip 40, respectively. Rollers 51, 52contact the upper and lower surfaces respectively of strip 40 at edge40A adjacent cross-feed line A-B. In similar manner, vertically spacedcarbide rollers 51A, 52A are rotatable on precision ball bearings aboutaxles 54, 54A respectively, above and below strip 40, respectively andcontact the upper and lower surfaces of strip 40 at edge 40B adjacentline A-B. Axles 53, 53A are affixed to one end of elongated outboardarms 55, 55A respectively, each of which is pivoted intermediately ofits length to fixed pivot 55B. The opposite ends of arms 55, 55A arefixed respectively to aluminum target plate 57 and sensor 58. A tensionspring 59 is coupled at its opposite ends to arms 55, 55A respectivelyto bias arms 55, 55A towards one another, maintaining contact betweenrollers 51, 52 and their respective surfaces of strip 40. Other armbiasing means may be used and spring 59 is diagrammatic. The lengths ofarms 55, 55A between their respective rollers 51, 52 and pivot 55B are afraction, e. g. one third, of their lengths between pivot 55B and targetplate 57, sensor 58, respectively, in order to provide a mechanicaladvantage and magnify the relative movement between rollers 51, 52,which is imparted by and a measure of the thickness of strip 40 at edge40A and increase sensitivity of the measurement. Sensor 58 is of thetype that can accurately measure the distance between its lower end andtarget plate 57. In similar manner, axles 54, 54A are affixed to one endof elongated outboard arms 56, 56A respectively, each of which ispivoted intermediately of its length to fixed pivot 56B. The oppositeends of arms 56, 56A are pivoted respectively to aluminum target plate57A and sensor 58A, mounted for sliding vertical movement, respectively.A tension spring 59A is coupled at its opposite ends to arms 56, 56Arespectively to bias the arms towards one another, maintaining contactbetween rollers 51A, 52A and their respective surfaces of strip 40.Other arm biasing means may be used and spring 59A is diagrammatic. Thelengths of arms 56, 56A between their respective rollers 51A, 52A andpivot 56B are a fraction, e. g. one third, of their lengths betweenpivot 56B and target plate 57A, sensor 58A, respectively, in order tomagnify the relative movement between rollers 51A, 52A, which isimparted by and a measure of the thickness of strip 40 at edge 40B toincrease sensitivity of the measurement. Sensor 58A is of the type thatcan accurately measure the distance between its lower end and targetplate 57A and provides strip 40 thickness measurements at each of edges40A, 40B and also a thickness differential between edges 40A and 40B.Sensors 58, 58A are commercially available from Kaman Instrumentation,P. O. Box 7463, Colorado Springs, Colo., 80933, their KD-4000 Series.

Damping rollers 60, 61 are placed above and below respectively and inpressure contact with strip 40 before the carbide sensing rollers anddamping rollers 62, 63 are placed above and below respectively and inpressure contact with strip 40 after the carbide sensing rollers to dampany vibration of strip 40 so that accurate thickness measurements arefacilitated. The signals from each sensor 58, 58A are read and averagedin gauge 50 providing an analog "front" and "back" reading for the frontedge 40A and the back edge 40B respectively. The two averages are thenaveraged in gauge 50 or controller 190, FIG. 5, later described, by anadditional averaging unit to provide an average strip 40 thickness.Sensors 58, 58A, may be contacting with rollers as shown,non-contacting, and electronic or air. In practice, it is preferable toclean strip 40 prior to gauging in any suitable manner known to the artand to use air jets on strip 40 immediately prior to strip 40 contact bythe sensing rollers to insure accurate measurements.

Gauge 50 is superposed and securely mounted on elongated bolster 64which extends longitudinally the length of assembly 42. Gauge 50 mayalso be placed elsewhere, e. g. between the strip 40 coil supply andassembly 42 since the thickness variations of strip 40 are sufficientlygradual that the measurement may be taken relatively close to assembly42 although not immediately before Station No. 1 as shown. Elongated dieshoe 66 is superposed and securely mounted to bolster 64 and extendslongitudinally between gauge 50 and the opposite longitudinal end ofbolster 64. Elongated die retainer 68 is superposed and securelyattached to die shoe 66 and extends longitudinally the length thereof.Elongated punch assembly 69 having elongated upper shoe 70 is superposedretainer 68 and is mounted for reciprocal vertical movement and isoperated in a press, not shown, for use with assembly 42 and iscommercially available, one source being Minster Machine Company,Minster, Ohio, 45865, Model P2 series, or equivalent, which includes afeed mechanism for strip 40 and punch press control 72, FIG. 5, laterdescribed. The press also includes a powered ram, not shown, controlledby punch press control 72, to operate shoe 70 downwardly to blank strip40 at each of Station Nos. 1-6.

At Station No. 1, a cluster of elongated vertical punch pins are mountedin and depend from shoe 70, pin 74 being shown, for blanking openings26. The cluster is secured to shoe 70 by depending set block 76, in amanner known in the art. The lower end of each pin in the cluster, andthe other depending pins and punches to be described at Station Nos.2-6, in the raised position of shoe 70 are above strip 40 and provideclearance for the progressive longitudinal movement of strip 40 throughthe stations assembly 42. Pin 74, and the other Station No. 1. clusterpins, are received for longitudinal movement in close fitting openingsin spring stripper 78 which depends from shoe 70 and is positionedimmediately above strip 40, extends longitudinally of Station Nos. 1 and2, and is mounted in conventional manner for stripping of strip 40 frompins of the cluster. In the punching stroke of shoe 70 the lower end ofpin 74 and the other cluster pins punch or blank openings 26 in strip40.

At Station No. 2, a pin cluster is mounted in and depends from shoe 70for blanking vent openings 28, pin 80 being shown, in conventionalmanner, the pins extending through corresponding close fitting openingsin set block assembly 82 which depends from and is secured to shoe 70.Assembly 82 carries a pin cluster of vertical and depending pins forblanking slot openings 24, pins 84, 86 being shown. The vent and slotopening pins, including pins 80, 84, 86, are received for verticalsliding movement in stripper 78 and extend into corresponding closefitting openings in a die retainer 68 during the punching stroke of shoe70.

At Station No. 3, depending counter bore punch 88 is carried in carriage90 which is mounted for reciprocal movement in bridge stripper 91.Carriage 90 is spring urged upwardly by a pair of compression springs 92which act between carriage 90 and stripper 91 which is supportedimmediately above strip 40 in conventional manner and extendslongitudinally of Station Nos. 4 and 5. Solenoid plate 96, shown insolid lines in its forward position, is mounted in shoe 70 forreciprocal movement longitudinally of shoe 70 as shown by double headedarrow 98 and is actuated by a solenoid, not shown. The retractedposition of solenoid plate 96 is shown by the dashed line 96a. Plate 96in its forward position displaces carriage 90 downwardly relative toshoe 70 against the force of spring 92 and in this position punch 88will blank out a counterbore opening 49 in strip 40 when shoe 70 is in apunching stroke. When plate 96 is in position 96a, carriage 90 is springurged upwardly relative to shoe 70 and in this position punch 88 willnot blank out a counterbore opening 49 in strip 40 on a punching strokeof shoe 70. Thus, by controlling the position of plate 96, an opening 49can be selectively made in strip 40.

Carriage 104 carries a cluster of elongated vertically dependinginterlock tab blank punch pins, pin 106 being shown. Carriage 104 hascenter bore 108 which slidingly clears punch 88 and carriage 104 isspring urged to an upward position relative shoe 70 by a plurality ofcompression springs acting between carriage 104 and stripper 91, spring114 being shown. A pair of solenoid arms 110, 112 are mounted in housing94, which securely depends from shoe 70, to move transversely alonglines CD, EF (FIG. 4) respectively, which lines are perpendicular to theline of feed of strip 40 and are actuated simultaneously by a solenoidmechanism not shown. When arms 110, 112 are in their extended positionas shown in solid lines, they are between shoe 70 and carriage 104displacing carriage 104 downwardly against the force of springs 114 inwhich position pins 106 are caused to blank interlock tab openings 48from strip 40. When arms 110, 112 are retracted to the dashed linepositions 110A, 112A, respectively, they are clear of carriage 104 andit is spring urged upwardly so that when shoe 70 is in a punchingstroke, interlock tabs 48 are not blanked from strip 40. Thus, byposition control of arms 110, 112 openings 48 can be selectively blankedfrom strip 40.

At Station No. 4, carriage 118 carries a cluster of vertically dependingelongated pins, pin 120 being shown, for lancing and forming interlocktabs 34. The lower end of pin 120, and the other carriage 118 clusterpins, has a bevel 122, FIG. 3C, which imparts a corresponding bevel toeach depressed tab 34. Mounted for reciprocal sliding movement inopenings in die shoe 66 and die retainer 68 beneath each carriage 118cluster pin, such as pin 120, is an elongated vertical upwardly springloaded supporting pin 124 against which tab 34 is formed to limit itsdepressed distance to one lamina thickness and prevent tab inclination.A spring 132 is mounted in die shoe 66 to provide the spring loading foreach pin 124. Solenoid plate 128, shown in solid lines in its forwardposition, is mounted just beneath shoe 70 for reciprocal movementlongitudinally of shoe 70 as shown by double headed arrow 130 and isactuated by a solenoid, not shown. The retracted position of plate 128is shown by dashed line 128A. Plate 128 in its forward positiondisplaces carriage 118 downwardly relative to shoe 70 against the forceof a plurality of compression springs mounted between stripper 91 andthe lower surface of carriage 118, spring 126 being shown. In thisposition each pin 120 will lance and form a tab 34 when shoe 70 is inits punching position. When plate 128 is in position 128A, carriage 118moves upwardly under the force of spring 126 and the other springs notshown and pins 120 will not lance and form a tab 34 on a punching strokeof shoe 70. Thus by controlling the position of plate 128, tabs 34 canbe selectively lanced and formed. All laminas 22 except the bottomlamina in core 20 have tabs 34 lanced and formed therein. It isunderstood that when it is desired to change the direction of the axesof slots 38 from right hand to left hand, a different cluster of pins106 and 120 will be used to change the direction of tab blank 48 andtabs 34 from counterclockwise to clockwise from their respective holes26.

At Station No. 5, laminas 22 are punched from strip 40 and shaft holes30 are simultaneously blanked and the slugs removed though chute 140,after which the laminas 22 are returned to the plane of strip 40.Cylindrical punch 136 is securely mounted in depending position from thelower surface of shoe 70 as by bolts, bolt 138 being shown, and isvertically slidably movable in an opening in spring stripper 139 whichdepends from shoe 70 in conventional manner and is supported immediatelyabove strip 40. Stripper 139 extends longitudinally of Station Nos. 5and 6. Punch 136 has an opening 141 for passing blanked slugs to chute140 which is supported by flange 143 which is bolted to shoe 70 as bybolts 143A. Chute 140 is shown 90 out of position in FIG. 3 forillustrative purposes. A cylindrical push back ring 142 is slidablymounted for vertical movement in an opening in die ring 151 and isupwardly biased by a plurality of compression springs, spring 148 beingshown, vertically slidably mounted in cylindrical block 144 which issecured in die shoe 66 by bolts, bolt 146 being shown. A plurality ofheavy compression springs 145 are mounted in bolster 64 and urge springblock 145A, mounted for vertical reciprocal movement in an opening inbolster 64, upwardly in the opening in bolster 64. Plate assembly 145B,FIG. 3D, is mounted for vertical reciprocal movement in an opening indie shoe 66 and is flush with and abuts the upper surface of block 145Aand houses the heads of a plurality of bolts, bolt 147 shown. Bolts 147extend through respective springs 148 and are in threaded engagementwith ring 142 so that ring 142 is spring urged upwardly. Flanged diering 151 is set in retainer 68 and limits the upward movement of ring142. Also mounted in block 144 is elongated vertical center shaft holepunch 150 which registers with opening 141. As shoe 70 descends in apunching stroke, a lamina 22 is blanked from strip 40 and shaft hole 30is blanked, the blanked slug being carried away through opening 141 andchute 140 as by applying a vacuum or reduced pressure therein. Lamina 22is returned to the plane of strip 40 by push back ring 142 after whichstrip 40 is advanced to carry lamina 22 to Station No. 6.

At Station No. 6, cylindrical punch 154 is affixed to, and depends from,shoe 70 as by bolts, bolt 156 being shown, and is vertically slidablethrough an opening in stripper 139. Flanged collar 162 is mounted in dieshoe 66 in a race of tapered bearings 158 for rotation about verticalaxis 160 and extends through an opening in die retainer 68. Areplaceable carbide choke ring 164 is press fitted into the upper end ofcollar 162 and rotates therewith. Spiral bevel ring gear 166 is affixedto the lower surface of collar 162 as by bolts such as bolt 168 androtatably drives collar 162 about axis 160. Spiral bevel pinion gear 170is in driving engagement with gear 166 and in turn is driven byservomotor 172, FIG. 5. Motor 172 is geared such that five motor shaftrevolutions equal one revolution of ring 164. On each punching stroke ofshoe 70, a lamina 22 is pushed from strip 40 into choke ring 164 whichis dimensioned to receive and hold a stack 21 of laminas 22 in africtional or interference fit, causing each of tabs 34 of the pushedlamina to engage and interlock with the corresponding tab openings andopenings 26 of the top lamina 22 in stack 21 to secure the two laminastogether in a given relative rotational position. After each downstrokeof shoe 70, servomotor 172 turns gear 170 a predetermined rotationaldistance to impart a rotational movement to collar 162 through ring gear166. The rotational distance is determined by the skew angle of the axisof slots 38 and on the thickness variations of strip 40, as is explainedmore fully herein.

The laminas 22 are continually stacked in ring 164 of collar 162, thelaminas in collar 162 building the stack 21 until a completed stack 21forms a rotor core 20. As the top lamina 22 is forcefully inserted ontostack 21, the other laminas are pushed downwardly a distance equal tothe thickness of a lamina. When all of the laminas in a stack 21 whichforms a core 20 have cleared choke ring 164, the core 20 drops onconveyor belt 176, FIG. 5, which carries the core 20 to anotherprocessing area. The core 20 height is determined by the number oflaminas 22 in a completed stack 21, which in turn is controlled by thenumber of laminas formed between two successive bottom laminas whichhave interlock tab blanks 48 formed therein. As explained, the bottomlaminas do not have tabs 34 formed therein and therefore will notinterlock with the next lower lamina thus providing separation ofsuccessive cores 20.

Referring now to FIG. 5, thickness gauge 50, bolster 64, die shoe 66,and shoe 70 are shown diagrammatically, shoe 70 being only partiallyshown. Power supply 180 has a three phase 60 Hz input on line 182 from aconventional source, not shown. Power supply 180 is available from KiowaCorporation, 7685 Corporate Way, Eden Prairie, Minn., 55344, Model No.8360, bus voltage +120 to +160 VDC, continuous current +/- 60 amps, peakcurrent +/- 100 amps, or equivalent. Supply 180 provides DC power to DCservomotor 172 through line 184 and receives motor 172 shaft rpm speedinformation from motor shaft coupled tachometer 186 on line 188 and acontrol signal from programmable controller 190 on line 192. Controller190 receives a motor 172 shaft rpm speed signal on line 193 from motor172 attached to tachometer 186 and motor 172 shaft angular position .oslashed._(p) on line 194 from motor 172 shaft coupled to optical encoder196. Motor 172, tachometer 186, and optical encoder 196 are of the typecommercially available from PMI Motors Inc., 5 Aerial Way, Syosset, N.Y.11791, Catalog No. MC24P, or equivalent. Encoder 196 provides 1000counts per revolution of motor 172 shaft so that there are 5000 countsfrom encoder 196 for each revolution of ring 164.

Controller 190 also receives thickness gauge 50 signals from sensors 58,58A, on line 198, which signals are also supplied to punch press control72 on line 200. Gauge 50 may be preset to a minimum thickness and amaximum thickness for each of T₁ and T₂ and when the thickness isoutside the minimum-maximum range of either of T₁ and T₂ fault signal issent on line 200 to press control 72 to stop the assembly 42 operation.Controller 190 receives a crank position signal from punch press control72 on line 201 to provide timing signals t_(a), t_(b), described below.Crank position defines the position of shoe 70 in its punching strokecycle. It is important that assembly 42 be coordinated so that punchingstroke of shoe 70 occurs only after all of the solenoid and rotationaladjustments have been made. Also, it is preferable that strip 40thickness readings by gauge 50 be made between punching strokes of shoe70 to minimize shock and vibrations during measurement.

Controller 190 provides an enable interlock tab blank 48 signal to thesolenoid for punch cluster arms 110, 112 at station No. 3 on line 202,an enable counterbore 49 punch signal to the solenoid for plate 96 atStation No. 3 on line 204, a disable interlock lance and form tabs 34signal to the solenoid for plate 128 at Station No. 4 on line 206, atiming signal to gauge 50 on line 208, and a stop press signal to punchpress control 72 on line 210 for stopping operation of die assembly 42,under certain conditions as described herein.

Prior to die assembly 42 operation, the press operator inputs thefollowing to controller 190:

II, Stack height of core 20;

A_(s), Skew angle of axes of slots 38 relative axis 32;

Skew direction (+=Clockwise, -=Counterclockwise) of slots 38;

Core 20 O.D. (outside diameter);

Counterbore 33 depth;

T_(N), Nominal lamina 22 thickness;

E_(p), Permissible parallelism error in core 20 stack;

Q, minimum number of stack 21 reversals (0, 1, 3, 5).

Note: if the number of laminas 22 that are to be reversed is preset, i.e. not to be automatically determined by the thickness variations sensedby gauge 50, then the operator inputs the desired number of stackreversals per core 20 during stacking that would provide the correctionfor the parallelism error and therefor it would not be necessary toenter the parallelism error. Also, even if the number of stack reversalsare automatically determined, the minimum number of reversals, Q, percore 20, may also be entered.

The dynamic inputs to controller 190 that are automatically input duringassembly 42 operation are as follows:

.o slashed._(p), the actual angular position of motor 172 shaft;

T₁, the thickness of strip 40 at point 40A;

T₂, the thickness of strip 40 at point 40B;

T₁ minus T₂, the differential of thickness of strip 40 at point 40A andthe thickness of strip 40 at point 40B;

t_(a), enable time for reading T₁ and T₂ on line 198, approximately 10ms;

t_(b), enable time for servomotor 172 drive, approximately 100 ms;

t_(c), enable time for outputs on lines 202, 204, or 206, approximately50 ms each.

In the operation of controller 190, initial thickness readings T₁, T₂are taken on line 198 during a 10 ms window at time t_(a), when strip 40is at Station No. 3 for the first lamina in the stack 21 and controller190 provides an average of thickness readings T₁, T₂ which is comparedto the operator entered input nominal stack height H to determine theapproximate number N of laminas per core stack. This approximate numberN is used to determine the number of lamina 22 deposited on stack 21before each reversal when the operator enters inputs for the minimumnumber of required reversals Q and to determine the incrementalrotations required to provide the operator input for skew angle A_(s).In addition, four arithmetic running totals are started. Two totals arebased on an average strip 40 thickness reading, and of these two, afirst total is not delayed and a second total is delayed by threeassembly 42 punch strokes of shoe 70 to reflect accumulated stack 21height or thickness at Station No. 6. A running total is also startedfor each of sensors 58, 58A in thickness gauge 50, one sensor at each ofstrip 40 edges 40A, 40B, and these totals are also delayed by threecounts or strokes of assembly 42.

The enabling of the interlock removal punch cluster at Station No. 3 online 202 occurs only on first or bottom lamina stroke in each core 20stack. The interlock lance and tab 34 form cluster, Station No. 4, isdisabled by a signal on line 206 only on the assembly 42 stroke when thefirst lamina, or bottom lamina, is at Station No. 4. The enabling of thecounterbore 33 punch 88 based on the above mentioned first total(undelayed average lamina thickness running total). Punch 88 is enabledon the first assembly 42 stroke for a new stack 21 and remains enableduntil such first arithmetic total is greater than the nominalcounterbore depth entered by the operator. Punch 88 is then disableduntil the assembly 42 stroke for the next first lamina in a stack 21. Ofcourse, if no counterbore thickness is entered by the operator, thenpunch 88 will always be disabled.

The rotation of die ring 164 in Station No. 6 is determined by: (1)operator inputs for (a) skew angle A_(s) (b) rotor O.D., (c) stackheight H, (d) skew direction, and when entered by the operator, (e)minimum number of stack 21 reversals, (f) parallelism error E_(p), and(2) Dynamic inputs for (a) accumulated differential between "front" edge40A and "back" edge 40B thickness accumulations, a reversal or half turnof ring 164 occurring when accumulated thickness differential exceeds afactor of the permissible entered parallelism error E_(p) ; a newdifferential thickness accumulation starts at each reversal of ring 164,and (b) sequential lamina 22 number "n" in a core 20 stack. Thesequential number n of laminas 22 in the stack 21 is used to determine adie ring 164 reversal when a minimum number of stack reversals Q isentered so that the reversals occur at predetermined intervals in thestack 21 as will be explained and described sore fully.

Controller 190 determines core stack 21 reversals as follows:

When the operator enters a number of stack 21 reversals (Q):

    ______________________________________    CONDITION              H    ______________________________________                 .sup.  n < (N/2Q = 1/2)                               0    (N/2Q - 1/2) < n < (N/2Q + 1/2)                               2500    (N/2Q + 1/2) < n < (1.5N/2Q - 1/2)                               0    (1.5N/2Q - 1/2)                 < n < (1.5N/2Q + 1/2)                               2500    (1.5N/2Q + 1/2)                 < n < (2.5N/2Q - 1/2)                               0    (2.5N/2Q - 1/2)                 < n < (2.5N/2Q + 1/2)                               2500    (2.5N/2Q + 1/2)                 < n < (3.5N/2Q - 1/2)                               0    (3.5N/2Q - 1/2)                 < n < (3.5N/2Q + 1/2)                               2500    (3.5N/2Q + 1/2)                 < n < (4.5N/2Q - 1/2)                               0    (4.5N/2Q - 1/2)                 < n < (4.5N/2Q + 1/2)                               2500    (4.5N/2Q + 1/2)                 < n           0    ______________________________________     Where:     M = counts of encoder 196 (Motor 172 is geared so that five shaft     revolutions = one revolution of ring 164 and encoder 196 counts 1000     counts per shaft revolution so that there are 5000 counts of encoder 196     for each revolution of ring 164);     N = H/T.sub.N  = nominal total number of laminas in a core 20 stack;     Q = number of operator entered minimum stack 21 reversals;     n = the particular lamina number in a core 20 stack where n = 1 for the     first lamina and n = N for the last lamina.

Where:

H=counts of encoder 196 (Motor 172 is geared so that five shaftrevolutions=one revolution of ring 164 and encoder 196 counts 1000counts per shaft revolution so that there are 5000 counts of encoder 196for each revolution of ring 164);

N=H/T_(N) =nominal total number of laminas in a core 20 stack;

Q=number of operator entered minimum stack 21 reversals;

n=the particular lamina number in a core 20 stack where n=1 for thefirst lamina and n=N for the last lamina.

When operation is automatic (no operator entered Q):

    ______________________________________    CONDITION         H    ______________________________________    ΣT.sub.1 - ΣT.sub.2 > +/- Ep/2                      2500    ΣT.sub.1 - ΣT.sub.2 > +/- Ep/2                      0    ______________________________________     Where:     T.sub.1 = Thickness measurement of strip 40 at edge 40A.     T.sub.2 = Thickness measurement of strip 40 at edge 40B.     Ep = Operator entered parallelism error.

Where:

T₁ =Thickness measurement of strip 40 at edge 40A.

T₂ =Thickness measurement of strip 40 at edge 40B.

E_(p) =Operator entered parallelism error.

In operation of controller 190 to determine the desired ring 164 angularposition, .o slashed., before interlocking the next lamina 22 on stack21, the accumulated rotational increments of ring 164 to obtain thedesired skew angle of slots 38 is added to H or half turn rotation thatwas determined i the manner immediately preceding. Thus,

    .o slashed.=5000 B.sub.S (S/H)+H

Where:

.o slashed.=in counts of encoder 196;

B_(S) a skew factor determined by controller 190 from the operatorentered skew angle A_(s) and is equal to the peripheral inches of skewbetween the top and bottom of a single slot 38 in a core 20/(core 20O.D.×pi); also, B_(S) =skew angle of a slot 38 axis/360°;

S=accumulated height of stack 21 in collar 162.

H=core 20 stack height.

H=counts of encoder 196 relating to state of half revolution of ring 164as determined above.

.o slashed. is compared with .o slashed._(p), received by controller 190on line 194, and if there is an error differential, an error signal isprovided on line 192 to power supply 180 which provides a correctionvoltage on line 184 to motor 172 to servo the error differential tozero, advancing or retarding the rotational position of ring 164 throughthe gearing.

Controller 190 determines the last lamina 22 in a core 20 stack by usingbinary signals, 0, 1, for L, which is the last lamina logic symbol:

L=0 when s<H-T_(N/2)

L=1 when s>H-T_(N/2)

S, H, and T_(N) are defined as before. If T_(N) is not entered by theoperator, then controller 190 uses T_(N) =(T₁ +T₂)/2, T₁ and T₂ beingdefined as before.

When L=1, controller 190 resets S, N, and n_(s), S and N being definedas before and n_(s) =short count, a count that is made by controller 190for timing signal t_(c) and is equal to n, defined as before. n_(s) isdisabled when n_(s) >2. When n_(s) =1, an enable signal for punchcluster to remove blanks 48 is provided on line 202 to the solenoid forarms 110, 112 for approximately 60 ms and when n_(s) =2, a disablesignal for punch cluster to lance and form tabs 34 is provided to thesolenoid for plate 128 for approximately 60 ms.

When

(C_(D) -S)>T_(N/2), an enable signal for counterbore punch 88 isprovided on line 204 to the solenoid for positioning plate 96. C_(D) isthe entered counterbore 33 depth and S and T_(N) are defined as before.

A signal for disabling punch assembly 42 is provided on line 210 tocontrol 72 when:

N/2Q<16

N and Q being defined as before.

Also, when either T₁ or T₂ is outside a preset minimum-maximum range afault signal on line 200 is sent to punch press control 72, assembly 42is stopped since strip 40 is too far out of thickness variationtolerance to be used.

Programmable controller 190 is commercially available from KiowaCorporation, address as above, and is designated Profiler II MotionController (modified) and includes:

(1) No. MIC 8201 Motor control module.

(1) No. MIC 8210 Digital positioning module.

(1) No. MIC 8100 Digital I/O module.

(1) No. MIC 2124 optically isolated I/O card with 24 I/O modules and DCpower supply.

(1) No. MIC 8408 Analog input module.

(1) No. MIC 2832 Alphanumeric display.

(3) No. TW-8 Thumbwheel programmers.

(1) No. REM-2 Remote programming panel.

(1) EXP-2 Dual Port I/O expansion module.

Custom software for programmable controller 190 is also commerciallyavailable from Kiowa Corporation, address as above, for operation ofcontroller 190 in the manner described above, and from other sources.

Referring to FIGS. 7 and B, gauge 50A is shown and which may be mountedrelative assembly 42 in the approximate position of gauge 50, FIG. 3, ormay be mounted outboard of assembly 42 in a cloaner environment and foreasier calibration. Lower housing 218 has lower base 220 to which issecured horizontally spaced upstanding lower mounting arms, arms 222,224 being shown, by n plurality of bolts, bolt 230 shown. Upper housing232 has upper base 233 to which is secured horizontally spaced dependingtipper mounting arms, arms 234, 236 being shown, by a plurality ofbolts, not shown. Housings 218, 232 are resiliently coupled by aplurality of bolt-spring combinations, combination 242 shown. Elongatedbolt 244 has its head fitted in a shouldered opening in arm 222 andextends vertically upwardly through openings in corresponding lower andupper mounting arms 222, 234, respectively, and extends above base 233where its threaded end is fastened to nuts 246, 248. Compression spring250 is fitted in facing shouldered openings in arms 222, 234, placingarms 222, 234 under a separating spring pressure. Since bolt-springcombinations similar to combination 242 in construction and mounting areplaced in similar manner in each pair of corresponding lower and uppermounting arms, the arms in each pair are resiliently urged apart adistance that is adjustable by adjustably positioning nuts 246, 248 ofeach bolt-spring combination longitudinally on their respective bolts,urging housings 218, 232 resiliently apart.

Vertically spaced elongated damping rollers 254, 256 each has itsopposite axle ends rotatable in trunnioned mountings in respectivemounting arms, the mounting of one axle end of roller 254 in arm 222being shown, FIG. 8. In like manner, each of vertically spaced elongateddamping rollers 262, 264 has its opposite axle ends rotatable intrunnioned mountings in respective mounting arms, the mounting of oneaxle end of roller 262 in arm 224 being shown. Rollers 254, 256, 262,264 each is preferably of a resilient material and nylon covered.Elongated strip 40 passes between and is dampened by rollers 262, 264and rollers 254, 256 which are in adjustably resilient contact withstrip 40 by adjusting the spacing between housings 218, 232 aspreviously explained.

Damping plates 270, 272 are positioned above and below strip 40respectively, plate 270 secured below base 233 by transversely spacedvertical arms, arm 274 being shown, and plate 272 secured above base 220by transversely spaced vertical arms, arm 278 being shown. Each ofplates 270, 272 has opposite cross feed edges that are tapered, one edgeof each plate extending between and spaced from rollers 254, 256 and theopposite edge of each plate extending between and spaced from rollers262, 264. Each of plates 270, 272 has a vertical clearance of between0.005-0.010 inches with its respective strip 40 surface to dampen strip40 flutter and thus limit the movement and vibration of the thicknessgauge rollers next described.

Gauge 50A has vertically spaced carbide rollers 292, 294, similar torollers 51, 52, FIGS. 3, 3A, rotatable on precision ball bearings abouthorizontal, transverse axles 296, 298, respectively, above and belowstrip 40, respectively. Rollers 292, 294 contact the upper and lowersurfaces respectively of strip 40 tit edge 40A. Axles 296, 298 areaffixed to one end of roller arms 300, 302, respectively, arms 300, 302fixed to pivot pins 304, 306 respectively. Pins 304, 306 are rotatableon precision ball bearings in upstanding post 308 fixedly supported onbase 220 between arms 222, 224. Fixed to the outboard ends of pins 304,306 are elongated gauge arms 312, 314 respectively, arms 312, 314 beingreplaceable for purposes later described. Opposed ends of arms 312, 314carry aluminum target plate 316, similar to target plate 57, and sensor318, similar to sensor 58, respectively. Spring loaded pin 320 isslidably mounted in upstanding block 322 which is fixedly mounted tobase 220 to bias arm 312 in a clockwise direction about pin 304 andspring loaded pin 324 is slidably mounted in block 326, which issupported in fixed relation to block 322, biasing arm 314 in acounterclockwise direction about pivot pin 306 to maintain contactbetween rollers 292, 294 and their respective surfaces of strip 40.Bolts 328, 330 fixedly support block 322 to base 220 and have upwardlyextending ends that act as rotational stops for arms 314, 312respectively. The distance between axle 296 and pin 304 is a fraction,e.g. one third, of the distance between pin 304 and target plate 316 andthe distance between axle 298 and pin 306 is a fraction, e. g. onethird, of the distance between pin 306 and sensor 318 in order tomagnify the movement between rollers 292, 294 which is imparted by and ameasure of the thickness of strip 40 at edge 40A and increasesensitivity of the measurement. Arms 312, 314 may be replaced with armshaving a greater distance between pins 304, 306 and plate 316, sensor318 respectively for greater sensitivity as is understood by thoseskilled in the art. In similar manner, carbide rollers and associatedsensor and target plate, not shown, are mounted on the oppositecross-feed side 40B of strip 40 to measure the strip 40 thickness atedge 40B and operate to provide in conjunction with sensor 310 outputsthe thickness measurement as described for sensors 58, 58A.

Modifications of this invention will be apparent to those skilled in theart. If supply strip 40 has a certain differential cross feed thicknessand experience shows that this differential exists over substantiallythe entire strip from a given supply coil, then only one or a relativelysmall number of thickness differentials need be read at gauge 50 andcontroller 190 can be set to determine the number Q of stack 21reversals per core 20 fabricated from that coil. Q, the minimum stack 21reversals per core 20 may be entered concurrently with selection of theautomatic reversal determination mode of this invention to insure aminimum number of stack reversals per core 20. Also, rotations of stack21 other than 180° may be made to accomplish the objectives of thisinvention, e. g. rotations of 90° to 270° could be used. The rotationsof stack 21 could be in increasing steps for successive stack rotations,e. g. 45° for the first rotation, 90° for the second rotation, 135° forthe third rotation, and so forth, adding 45° rotation to each successiverotation. To correct for a parallelism error E_(p), at least oneaccumulated reversal of stack 21 would be made. The thicknessmeasurements T₁, T₂ may be made at other points in the manufacturingprocess as long as they are timely made for determination of thereversals of stack 21 during stacking of the lamina and can be made ofthe lamina itself after being blanked from strip 40. Further, thisinvention can be used to advantage in the manufacture of other laminatedparts than those described herein. In like manner, other of the abovedescribed parameters may be varied to suit a particular set ofconditions for use of this invention.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. An apparatus for manufacturing electric motorparts from a sheet of stock material, said apparatus comprising:ablanking station; a stacking station; a sheet stock guide for guidingsheet stock material to said blanking station; a blanking punch at saidblanking station for blanking generally planar laminas from said sheetstock material, each said lamina including interlocking means and havingan axis substantially perpendicular to the lamina plane; a choke ringand associated stacking punch at said stacking station whereby laminasare received, stacked and individually interlocked to one another toform an interlocked stack having a central axis substantially coaxialwith said lamina axes; and a servo motor coupled to said choke ring forproviding rotation of at least one of said laminas and said stackrelative to one another, about said stack axis, prior to stacking saidat least one lamina through an arc within an arcuate range of 30° to330°.
 2. The apparatus according to claim 1 wherein said relativerotation is approximately 180°.
 3. An apparatus for manufacturingelectric motor parts from an elongated sheet of stock material, saidapparatus comprising:a blanking station; a stacking station; a sheetstock guide for guiding said sheet stock material to said blankingstation; a blanking punch at said blanking station for blankinggenerally planar laminas from said sheet stock material, each saidlamina having an axis substantially perpendicular to the lamina plane; achoke ring at said stacking station whereby laminas are received andstacked to form a stack having a stack axis substantially coaxial withsaid lamina axes; an interlock punch at said blanking station forproviding said laminas with interlocking means; a stacking punch at saidstacking station for interlocking said laminas to form an interlockedstack; and a servo motor coupled to said choke ring at said stackingstation for providing relative rotation of at least one of said laminasand said stack about said stack axis, prior to stacking said at leastone lamina through an arc within an arcuate range of approximately 30°to 330°.
 4. The apparatus according to claim 3 wherein said relativerotation is approximately 180°.
 5. An apparatus for manufacturingelectric motor parts from a sheet of stock material, said apparatuscomprising:a blanking station; a stacking station; a sheet stock guidefor guiding sheet stock material to said blanking station; a blankingpunch at said blanking station for blanking generally planar laminasfrom said sheet stock material, each said lamina including interlockingmeans and having an axis substantially perpendicular to the laminaplane; a choke ring and associated stacking punch at said stackingstation for receiving, stacking and substantially simultaneouslyinterlocking said laminas to form an interlocked stack having a centralaxis substantially coaxial with said lamina axes; and a servo motorcoupled to said choke ring for providing rotation of at least one ofsaid laminas and said stack relative to one another, about said stackaxis, prior to stacking and interlocking said at least one lamina, andto thereby compensate for thickness variations which occur in said sheetstock material.
 6. An Apparatus for manufacturing electric motor partsfrom sheet stock material, said apparatus comprising:a die including afirst stamping punch for stamping generally planar laminas, each laminahaving an axis substantially perpendicular to the lamina plane, and asecond stamping punch for stamping arcuately spaced conductor slotopenings in said lamina, said openings being radially spaced from theaxis of each of said laminas; a choke ring for coaxially stacking saidlaminas to form a stack having a predetermined height and stack axissubstantially coaxial with said lamina axes, said stack axis beingsubstantially perpendicular to the plane of each of said laminas; aservo motor for automatically incrementally rotationally indexing eachof said laminas and said stack relative to one another, about said stackaxis, through an arc so that said conductor slot openings form conductorslots having slot axes skewed to said stack axis by a predetermined skewangle; and a controller coupled to said servo motor to automaticallydetermine said arc by utilizing stack height.
 7. A die apparatus formanufacturing electric motor parts from a sheet of stock material, saiddie apparatus comprising:a blanking station; a stacking station; ablanking punch at said blanking station for blanking generally planarlaminas from said sheet stock material, each said lamina includinginterlocking means and having an axis substantially perpendicular to thelamina plane; a choke ring at said stacking station for receiving andstacking said laminas to form an interlocked stack having a central axissubstantially coaxial with said lamina axes, said choke ring beingrotatable within said die apparatus; and a servo motor coupled to saidchoke ring for providing rotation of said choke ring so that at leastone of said laminas and said stack are rotated relative to one another,about said stack axis, prior to stacking said at least one lamina,through an arc in the range of 30° to 330°.
 8. An apparatus formanufacturing electric motor parts from sheet stock material, saidapparatus comprising:a die including a first punch for stampinggenerally planar laminas, each lamina having an axis substantiallyperpendicular to the lamina plane, and a second punch for stampingarcuately spaced conductor slot openings in said lamina, said openingsbeing radially spaced from the axis of each of said laminas; a chokering for coaxially stacking said laminas to form a stack having apredetermined height and stack axis substantially coaxial with saidlamina axes, said stack axis being substantially perpendicular to theplane of each of said laminas; a servo motor for automaticallyincrementally rotationally indexing each of said laminas and said stackrelative to one another, about said stack axis, through an arc; and acontrol coupled to said servo motor rotating means for automaticallydetermining said arc.